1. Field Of The Invention
This invention relates to downhole testing apparatus having pumps used for inflating inflatable packers, and more particularly, to a testing apparatus with a single piston positive displacement diaphragm inflatable packer pump.
2. Description Of The Prior Art
A known method of testing a well formation is to isolate the formation between a pair of inflatable packers with a flow port therebetween adjacent the formation. The packers are inflated by means of a pump in the testing string which pumps well annulus fluid or mud into the packers to place them in sealing engagement with the well bore. A variety of such pumps are available.
One type of downhole pump is actuated by the vertical reciprocation of the tubing string connected to the pump. Such a pump is disclosed in U.S. Pat. No. 3,876,000 to Nutter and U.S. Pat. No. 3,876,003 to Kisling, III. This method of reciprocation results in many operational problems, and so other pumps have been developed which are operated by rotation of the tubing string relative to the pump structure connected thereto.
One type of rotationally operated pump uses a plurality of vertically reciprocating pistons which are driven by a cam structure. Inlet and outlet valves are positioned adjacent each of the pistons. Typical multiple piston pumps are disclosed in U.S. Pat. No. 3,439,740 to Conover and U.S. Pat. No. 4,246,964 to Brandell, both of which are assigned to the assignee of the present invention. These types of pumps require precise machining and assembly which are relatively expensive and susceptible to damage by impurities in the well fluid. In particular, the valves for such pumps can be relatively easily clogged.
A simpler, sleeve-type pump piston is used in the downhole pump of Evans et al., U.S. Pat. No. 3,926,254, assigned to the assignee of the present invention. This pump uses a plurality of sealing rings of V-shaped cross section for intake and exhaust check valves. In the Evans et al. apparatus, as well as the other pumps described above, the pump piston is in direct contact with the well annulus fluid which because of impurities therein can result in reduced service life.
The downhole pump of the testing apparatus of the present invention uses the more simple sleeve-type pump piston and further includes a diaphragm which separates a piston chamber in which the piston reciprocates from a pumping chamber with inlet and outlet valves therein through which the well fluid is moved to inflate the packers. The piston chamber is filled with a clean hydraulic lubricant which promotes longer life for the pump parts. Back-up piston wiper rings are provided to clean the piston of abrasive particulate in the vent that the diaphragm is ruptured.
Simple inlet and outlet check valves with resilient annular lips are used in the present invention which are not easily clogged or damaged by abrasives in the well fluid. These valves are similar to valves in the Halliburton Omni RS Circulation Valve, assigned to the assignee of the present invention and described in co-pending application Ser. No. 797,375 filed 11/12/85.
Most of the pumps of the prior art include relief valves which relieve pressure from the pump to the well annulus. A pump without a relief valve is disclosed in U.S. Pat. No. 4,313,495 to Brandell, assigned to the assignee of the present invention. In this pump, a clutch is used which is disengaged when the pump pressure reaches a predetermined level, thus making the pump inoperative.
The present invention utilizes a pressure limiter which vents around the outlet check valve to the packers at the lower end of the testing string rather than to the well annulus.